It is well known that a machine, such as a skid steer loader, typically includes a boom or liftarm stop member. The stop member is normally used to retain a lift cylinder in an extended state which holds the liftarm in a raised position, generally for specific machine repair purposes. Disengagement of the stop member usually requires that the lift cylinder be extended and the stop member manually moved to an inoperative position in order to lower the liftarm. Some designs, however, have utilized an automatic retraction system on the stop member to avoid the manual movement of the stop member to the inoperative position.
A design disclosed in U.S. Pat. No. 5,634,762 issued to In K. Kim on Jun. 3, 1997 utilizes a prop arm hingedly attached to a boom for swinging movement between a rest position parallel to the boom and a propping position in a bearing engagement with the distal end of a boom cylinder housing to maintain the boom in a raised position against retraction of a boom cylinder piston rod. A release lever is pivotally attached to the free end of the prop arm and movable between an idle position in which the release lever is folded back onto the prop arm, an unfolded position in which the tip end of the release lever rides on the cylinder housing, and an arm lifting position in which the release lever bears against the piston rod at the tip end thereof to lift the prop arm out of engagement with the distal end of the cylinder housing. The pressure and action of the release lever while riding along the cylinder housing causes damage to the outer surface of the cylinder housing. Additionally, the utilization of the prying action of the release lever against the cylinder housing may damage the cylinder. Furthermore, the orientation and positioning of the release lever on the prop arm may promote buckling of the release lever and subsequent necessity for replacement.
A design disclosed in U.S. Pat. No. 5,009,566 issued to James E. Asche on Apr. 23, 1991 utilizes a retractable boom stop. The retractable boom stop is movable between an inoperative position adjacent the boom arm and an operative position interposed between the boom arm and lift cylinder. The stop member is secured in the inoperative position by a retaining pin. A tension spring carried by the stop member and releasably securable to the boom arm automatically retracts the stop member out of the operative position to allow the lift cylinder to be retracted. The utilization of the tension spring may require frequent replacement for wear on the spring brought about by extended usage. Additionally, in some harsh environments, the spring may not function properly which may lead to increased operator involvement in retracting the boom stop. Furthermore, the high tension on the spring, which is necessary for proper functioning, may be difficult to "stretch" into operation and may, thereby, cause pinching to an operator's fingers.
The present invention is directed to overcoming the problems as set forth above.